Archive for the ‘Circuit Protection’ Category

Marine electrical questions?

Marine Ac/Dc attempts to answer your questions about boat wiring and marine electrical techniques, concepts, and products. We get lots of mail from folks in mid-project or who are just curious about their boat’s electrical setup.

There are loads of post already on the site which we hope you will browse through. If you’re trying to track down info about a more specific category, please use the search box in the upper right of this page or check out the list of various subjects farther down on this page.

If you aren’t able to find the info that you need to complete your particular boat wiring project, please send us an email at

Thank you for visiting. We look forward to hearing from you and hope that you will be able to come back often.

Floating Green?


I have just purchased a 7KVA generator set to replace my old one on my marine electrical system. The unit is supplied connected M.E.N. internally with output supply connected to a bipole circuit breaker.

As the connections between earth and neutral is before the the breakers, there is no allowance for the earth wire from the appliance side to connect to on the genset. Should I wire this appliance earth onto the frame of the genset or leave it ‘floating’?Westerbeke Generator


Hi A.T.,

The green, earth wire from your AC system needs to be connected to the chassis of the new generator. It should not be floating. With AC systems, the neutral and ground are connected at the source of power (the generator). The neutral and ground remain separate on the rest of the boat. The neutral is connected through the breaker and the ground directly.

The reality is, once the generator battery ground is connected to the rest of the battery negatives on the boat, the green, earth wire path is complete. Your AC system green earth wire is already connected to the boat’s DC negative system. The negative generator cable is connected to the generator ground. The generator ground is connected to the generator’s earth ground.

Hope this helps,


Stop Smoking


I tore all of the boat wiring out of my 1989 Champion. I have all new gauges and a new marine electrical switch panel.

When I attempt to hook up the new stuff to the – and + battery terminals, I get big sparks and smoking.

Have you got any suggestions?Smokin'



Hi George,

It sounds like there is a directly short to ground in your marine wiring.

Follow the + wire from the boat battery to the distribution. Check for proper connections on switch lights and crossed connections on gauges.

When you fix the problem, I strongly recommend adding circuit protection at the battery. It will trip before the smoke gets too thick.

Good luck,


Easy AC Outlets?


I am converting a barge into a houseboat/floating home.

I like the Easy Add AC Shore Power system that you designed for your retail marine electrical site, but want/need more electrical outlets to power things like computers, microwave, etc., etc…

Do you have a system that will handle more outlets or can you can you point me somewhere that I can find the information.

Thank you,


Hi Tim,

The complete shore power system can be expanded to as many outlets as you wish.

The limiting factor is the 20 amp main breaker. If 20 amps is not large enough, I would take a look at the panels that are available from Paneltronics. Their systems are not snap together marine electrical like ours, but they do offer a wide variety of AC panels.

Thank you,


House Battery Bank

Hello Kevin,

Thanks for all of your really helpful boat wiring advice.

I am rebuilding my boat battery wiring to add a dedicated house battery system.

I want to use six 6 volt lead acid batteries and want to wire them in a series/parallel configuration – but am confused about how each battery is inter-connected with the one next to it. They will sit in two rows of three batteries each. Boat battery wiring

Would you have a boat wiring diagram showing how to wire this up for six marine batteries?



Hi Charles,

Dedicated house battery systems are becoming more popular in marine electrical and for good reason. They can really help with power management and – more importantly – can make sure that you can start your engines to get home after a long day playing. This is especially true of boat battery wiring that includes an automatic smart boat battery switch.

Here is a boat wiring diagram that should help your with your project.


Wrong Charger?

Hi Kevin,

I hope you can help me with a boat wiring issue.

On my boat battery wiring, I have two batteries for my trolling motor, a 24 volt Motorguide. They are hooked up20 amp breaker

  • + to motor
  • - on battery to + on 2nd battery
  • - to trolling motor

The on board marine electrical battery charger has connections for two batteries. Do I just hook it up positive and negative on both batteries?

The reason I ask is the in line fuse on one battery was blown as I took it apart today.



Hi Dean,

Most dual output battery chargers are designed to be connected the way you had them.

The blown fuse may just be a fluke or your charger may not be designed to charge your batteries in series. Check with the manufacturer’s recommendations. If they say 12/24 volt systems, then you are good to go. If not, you will need to disconnect the batteries to charge or buy another charger.


Euro boat on US shore power?

Hi Kevin

I brought my sailboat from Europe with me when I came here to work this year. The marine electrical is completely European spec, i.e., 220VAC-16A-12VDC. I am wondering how I can plug in to US shore power at marinas here in the US.Marinco adaptor

I do not want to completely change my boat wiring as I will eventually be returning to Europe. Also I am not a heavy user of power, I could cope with just keeping the batteries charged up.



Hi Paul,

Some of the AC components on your boat may be able to cope with the change in voltage and frequency, but not all of them and the solution is not as simple as adding a transformer to increase the voltage.

If you only want to charge your batteries, I would buy a simple battery charger and charge your batteries with an extension cord while the boat is in the states.

Good luck,


Bigger Breaker


When replacing my factory installed circuit breakers, I noticed the breaker for the bilge pump is only rated at 4 amps.

My Rule bilge pump, (also factory installed) is labeled “12 Volt 6 amp fuse”. The specifications I found on line say this pump draws 3.3A at 12 volts and 5.0 amps at 13.6 volts. I assume the boat wiring size used is typical for bilge pump installation. (appears to be 14-16 Ga.?) Carling breaker

Should I install a larger circuit breaker with this set-up? I am thinking a 7 Amp would be sufficient?

The boat is a 2002 Sea Pro 235 WA with two batteries.

Thank You


Hi Shonna,

I would go with the 7 amp breaker.

7 amps will not exceed the current carrying capacity of your wire, will help reduce nuisance tripping of the breaker under full load, but will trip under a locked rotar condition.



Glen-L Wiring


I am building a 16′ wooden bass boat using the Glen-L design and it is about 80% complete. I am now getting ready to outfit the interior, build the helm, purchase my motor, etc.

I have visited your sister boat wiring site and it looks like just what I will need due to its simplified “plug and play ” approach. What I am looking for is advice on everything I will need to wire my boat using EzAcDc marine electrical.

My boat wiring needs include:

In summary, I need everything and look to your recommendation to help me get what I need to fully wire my boat from the boat wiring harness to fuses, circuit breakers, switches, etc.

Thank you.


Hi Kelly,

Your boat sounds great! Thank you for your interest in the products at our sister site.

Here is the boat wiring that I would recommend.

  • Fully wired eight switch marine electrical panel. This comes with one panel mounted 12 volt receptacle and you will want to add a second remote outlet.
  • Boat wiring harness that quickly snaps together with the panel above.
  • Smart Battery Switch system for two batteries. This includes cables, ground bus, and you will want to add a couple of battery boxes.
  • Navigation lights are controlled by the nav/anc switch in your new switch panel. Wiring for split red and green lights and a single white stern light is included with the boat wiring harness. The site has a variety of Attwood LED navigation light kits that may suite your needs. All come with connectors so that they will snap right onto the new harness.
  • I would run 8 AWG tinned wire for your trolling motor.
  • Please send me the specs and length of total wire run for the power winch to determine the cable size requirements.
  • Currently we do not stock a trolling motor connection. My preference in the Marinco Connect Pro System.
  • You can use one of the switches on the new panel for the stereo. The new panel will even include a pre-printed “STEREO” switch cap. There is a ground, constant power (memory), and switched power coming off of the back of the switch for a stereo. We do not include speaker wire.
  • The boat wiring harness has two breakouts for courtesy lights. The switch panel kit also includes a “COURTESY LIGHTS” switch cap.
  • We do not have fish finders, but you can get power for your fish finder from one of the breakers on your new switch panel.
  • The switch panel comes pre-wired with a horn button and the boat harness includes wiring for a horn.
  • We also have boat horns that will attach easily onto the new harness.
  • We do not have gauges. Most of the gauge wiring will be included with your engine harness.
  • Our harness comes with one bilge pump and auto float switch connection. You can either run a second pump from one of the switch panel accessory wire breakouts or you can use the livewell pump breakout for a second pump.
  • No additional fuse panel is needed. The switches have circuit breakers mounted directly below them on the panel. The main harness battery connection has an in-line circuit breaker for harness protection.

Thank you again for your consideration. I hope this helps,



My boat anchor winch is the Deck Mate 19 Small Boat Anchor Windlass from West Marine. The draw is 15 amps @ 12 volts and the winch includes a built in 15A circuit breaker. The length of wire from the helm to the power winch at the bow is roughly 9 feet. Please advise cable size requirement.

Thank you.


Hi Kelly,

18′ run total @ 15 amps with 3% drop, I would run 10 AWG wire.


Columbia Rewire

Hello Kevin,

I’ve recently became the owner of a Columbia 22 sailboat built in 1969. I’ve gutted the boat wiring from her and need to rewire.

I need bow port and starboard navigation lights and some minor interior lights she currently has a white masthead light at the cross tree and a transom light. Both of them seem to look fine however I would like to convert to LED for all the lighting.Attwood is the world's top supplier of navigation lights for boats

She also has in place a Guest battery switch

I’m considering buying everything that I need from your snap-together boat wiring site.  But, before I do, can you tell me everything that I will need?

I think I need to control three separate lighting systems

  1. The red and green bow lights
  2. Masthead and stern
  3. Interior lights
  4. Perhaps nav/GPS and cell phone charger?

Any help would be appreciated. Your snap together wiring system seems like a real timesaver, but I didn’t want to get the wrong parts.

Finally, do you also furnish instructions on how it all hooks up to everything including battery?

Thanks again


Hi Peter,

I would start with our smaller boat wiring harness. This will provide wiring for your red/green boat lights, your white, all-round light, and interior lights.

On your boat, I would combine this harness with our five switch marine electrical panel. This panel will provide switches for your nav/anc and stern lights along with your cockpit courtesy lights.

We have several navigation light kits that plug directly into our wiring harness. Simply choose the mounting configuration for your boat.

The installation is easy and instructions are provided.

I would keep the Guest battery switch in the system. The main power connection from your new boat wiring harness will connect to the battery switch to allow you to completely turn the power off when you leave your boat.

Hope this helps,